Introduction to PsychToolbox in MATLAB
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Transcript of Introduction to PsychToolbox in MATLAB
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INTRODUCTION TO PSYCHTOOLBOX IN MATLAB
Psych 599, Summer 2016
Jonas Kaplan, Ph.D.University of Southern California
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Week 5 Recap
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Sound data
■ Sound data should be in the form of a matrix where each row is one sound channel
■ Samples in the vector should range from -1 to 1, where 0 is silent. ■ You can create a sound by generating data for a matrix on your own,
or you can read in from a wav file
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Reading from wav files
Y = wavread(FILE)[ Y, freq ] = wavread(FILE)
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Reading from audiofiles
[Y, freq ] = audioread()
New Matlab command available in versions 2012b and later, will read many audio formats including WAV, FLAC, MP3, MPEG-4, OGG
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Preparing sound data for playing>> whos funkData Name Size Bytes Class Attributes
funkData 624000x1 4992000 double
>> funkData = funkData'>> funkData = [funkData; funkData];>> whos funkData Name Size Bytes Class Attributes
funkData 2x624000 9984000 double
change column to rowduplicate to make two rows for stereo
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Steps to playing a sound
■ InitializePsychSound■ open audio channel with PsychPortAudio('Open')■ fill audio buffer with PsychPortAudio('FillBuffer')■ start playing a sound with PsychPortAudio('Start')■ stop playing a sound with PsychPortAurio('Stop')■ close the audio channel with PsychPortAudio('Close')
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Step 2: Open audio channelpahandle = PsychPortAudio('Open' [, deviceid][, mode] [, reqlatencyclass][, freq][, channels] [, buffersize] [, suggestedLatency][, selectchannels][, specialFlags=0]);
how aggressively to take over the sound device in order to assure latency
requested playback rate in Hz
playback channels:1 = mono2 = stereoetc.default is 2
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Step 3: Fill the audio buffer
PsychPortAudio('FillBuffer', pahandle, bufferdata);
This is analogous to drawing on the back buffer with the Screen command. We fill the buffer now, but it will not be heard until we play it.
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Step 4: Start playback
startTime = PsychPortAudio('Start', pahandle [, repetitions=1] [, when=0] [, waitForStart=0] [, stopTime=inf] [, resume=0]);
Wait until this time to start playing (default is play now)
Set to 0 to repeat indefinitely
set a time to stop playing0: Ask playback to
start and move on1: wait for playback to actually begin. A 1 here is necessary if you want to get timing info back
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Remaining steps
■ Stop playback if necessary: PsychPortAudio('Stop',pahandle);■ Close the audio driver:
PsychPortAudio('Close',pahandle);
Remember: Do not close audio channel before the sound is finished playing if you want to hear it all
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Sound recording steps
■ Initialize sound driver: InitializePsychAudio■ Open audio channel for recording with PsychPortAudio('Open') setting
mode to 2■ Clear a buffer using PsychPortAudio('GetAudioData')■ Start recording with PsychPortAudio('Start')■ Stop recording with PsychPortAudio('Stop')■ Get audio data using PsychPortAudio('GetAudioData')
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Step 2: Open audio channelpahandle = PsychPortAudio('Open' [, deviceid][, mode] [, reqlatencyclass][, freq][, channels] [, buffersize] [, suggestedLatency][, selectchannels][, specialFlags=0]);
1: sound playback only (default)2: audio capture3: simultaneous capture and playback (may not work on all hardware)
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GetAudioData
[audiodata absrecposition overflow cstarttime] = PsychPortAudio('GetAudioData', pahandle [, amountToAllocateSecs] [, minimumAmountToReturnSecs][, maximumAmountToReturnSecs] [, singleType=0]);
Call before you start recording to setup an empty buffer, then after recording to retrieve recorded data
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Writing data to file
wavwrite(audiodata, freq, nbits, filename)audiowrite(filename, audiodata, freq)
NOTE: for writing to file, audio channels must be in columns, not rows, so
you will have to transpose them again.
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Collecting responses
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Listing devices
devices = PsychHID('Devices');
• Returns a structure array where each element describes a single device
• PsychHID only checks for USB devices on startup. If you plug in a device after starting matlab it wont be recognized by PsychHID, even if you can see its input on the screen. You need to either restart Matlab or issue clear PsychHID to renumerate the connected devices.
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Psychtoolbox Response Monitoring
■ GetChar()■ KbWait()■ KbCheck()■ KbQueueCheck()
GamePad() GetMouse() GetClicks() GetMouseWheel
() SetMouse() ShowCursor() HideCursor()
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Keyboard responses
GetChar()
KbWait()
KbCheck()
KbQueueCheck()
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GetChar
[ch, when] = GetChar()
GetChar can return characters that were type before you called it!As long as listening is turned on, GetChar will be listening. It will then return all the keys pressed since it started listening, in order. If there are none left in the queue, it will wait for a new one.
Use FlushEvents() to clear the queue and to start listening. You can also call ListenChar() to turn listening on and off directly.
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KbWait
[secs, keyCode, deltaSecs] = KbWait([devicenumber] [, forWhat = 0][, untilTime=inf)
which device are we listening to?use PsychHID('Devices') to list all devices
GetKeyboardIndices() will return the device numbers of all keyboard devices
Use -1 to listen to all keyboardsUse -2 to listen to all keypad devicesUse -3 to listen to all keyboards and keypads
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KbWait
[secs, keyCode, deltaSecs] = KbWait([devicenumber] [, forWhat = 0][, untilTime=inf)
0: Default. Listen for key down1: Listen for key release2: Wait until all keys are released, THEN wait for key down3: Wait until all keys are released, then wait for a full key press and release
Stop waiting when we get to this time
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inside KbWait.m
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KbCheck
[keyIsDown, secs, keyCode, deltaSecs] = KbCheck([deviceNumber])
Has a key been pressed?1 if any key has been pressed, 0 otherwise
Time key was pressed
256-element logical vector indicating which key(s) were pressed
interval between this check and the last one
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Ignoring responsesDisableKeysForKbCheck([disablekeys])
vector of key codes to ignore
RestrictKeysForKbCheck([enablekeys])
vector of key codes to include
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waiting for a specific response
waiting for any response EXCEPT certain keys
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KbQueueCheck
■ An alternative set of commands for collecting keypresses:– KbQueueCreate– KbQueueStart– KbQueueStop– KbQueueCheck– KbQueueWait– KbQueueFlush– KbQueueRelease
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KbQueueCheck■ Advantages of KbQueueCheck:– Sometimes detects really brief responses that KbCheck
can miss– Very accurate time recording– Records presses and releases both■ Disadvantages:– Difficulty in recording multiple presses of the same key– May not deal well with many rapid keypresses
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Steps to using KbQueue
■ KbQueueCreate([deviceNumber]) to create the queue. ■ KbQueueStart() to start listening■ KbQueueStop() to stop listening (does not clear the
queue)■ KbQueueCheck() to check the values recorded while the
queue was active■ KbQueueFlush() to empty the queue■ KbQueueRelease() to destroy the queue object
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KbQueueCheck[pressed, firstPress, firstRelease, lastPress, lastRelease] = KbQueueCheck()
has a key beenpressed?
array indicating when each key was first pressed
array indicating when each key was first released
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Mouse responses GetMouse() GetClicks() GetMouseWheel
() SetMouse() ShowCursor() HideCursor()
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Mouse responses[x,y,buttons] = GetMouse([windowPtrOrScreenNumber][, mouseDev])
which mouse device
vector of three numbers, one for each mouse button0 = not pressed1 = pressed
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Other input devices
GamePad()
Type Gamepad in the command window for help, or Gamepad Subcommand? for help with a subcommand
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Gamepad■ Gamepad('GetButton',gamepadIndex, buttonIndex) to get
status of buttons■ Gamepad('GetAxis',gamepadIndex,axisIndex) to get joystick
position■ Gamepad('GetBall',gamepadIndex,ballIndex) to get
trackball info
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Assignment #5■ Create a function called yourinitials_week5()– The function will take one input, radius, which will determine the
radius of a circle – Draw a black circle in the center of the screen. Using KbCheck,
wait for the user to press a key. If the user presses R, the ball will turn red; if they press G the ball should turn green; B will turn the ball blue.
– The ball will begin moving towards the mouse position. Only move the ball 2 pixels each frame, do not jump right to the location of the mouse. The ball will follow the mouse around the screen until the user clicks the mouse, when the program will end and the screen will clear.
– While the ball is moving, the user may press R, G, or B to change the color of the circle accordingly.
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Week 6• DAQ toolbox• Randomization, permutation, condition order• Priority handling• Handling complex code: Subfunctions
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DAQ toolbox
■ DAQ = Data Acquisition device■ For communicating with the USB-1208FS from
Measurement Computing■ Allows input and out of digital and
analog signals
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Using the DAQ to synchronize
external measurement system
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Daq functions
■ Type "help DaqFunctions" to see all the PsychToolbox DAQ functions
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Sending output with the DAQ
■ 1. Identify the DAQ device in the PsychHID device list■ 2. Initialize the DAQ device with DaqDConfigPort()■ 3. Send output with DaqDOut()
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Finding your DAQ devicedevices = PsychHID('devices');daqIndex = 0;DAQFound = 0;
for i = 1:length(devices) if strcmp(devices(i).product,'USB-1024LS') daqIndex = i; endend
daqIndex = DaqDeviceIndex();
OR
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Communicating with the DAQ device
■ Digital vs Analog connections:DaqAInDaqAOutDaqAInScan
DaqDInDaqDOutDaqDInScan
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Initializing a portDaqDConfigPort(DeviceIndex, port, direction)
device index of the Daq device
which port you want to configure
0 = output1 = input
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Sending output
DaqDOut(DeviceIndex, port, data)
value you want to send to the output channel
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Example
■ Send a pulse to the Biopac (physio measurement) computer when the script receives the first trigger pulse from the MRI scanner in order to synchronize measurement among the devices
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Randomization
■ On startup, Matlab initializes the random number generator. ■ The rng creates a sequence of random numbers called the global
stream. ■ The random number functions (rand, randi, randn) access this list of
numbers, in order
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Randomization
■ rng controls the random number generator
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Randomization>> rng
ans =
Type: 'twister' Seed: 0 State: [625x1 uint32]
>> rng default>> randi(100,[1,10])
ans =
82 91 13 92 64 10 28 55 96 97>> rng default>> randi(100,[1,10])
ans =
82 91 13 92 64 10 28 55 96 97
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Randomization
■ "Seed" the random number generator to generate different values■ Common seed to use is the current time■ rng shuffle to reseed with current time
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Randomization>> rng shuffle>> rng
ans =
Type: 'twister' Seed: 2062320423 State: [625x1 uint32]
>> rng(1)>> rng
ans =
Type: 'twister' Seed: 1 State: [625x1 uint32]
>> rng(5,'combRecursive')>> rng
ans =
Type: 'combRecursive' Seed: 5 State: [12x1 uint32]
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Permutation
■ Matlab function randperm() and PTB function Shuffle() are useful for permuting lists
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Permutation
■ randperm(N) will create a vector of numbers from 1 to N in random order.
■ You can use these numbers as indexes to reference multiple lists in the same random order
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Permutation
■ Example:– You have a list of fruits, and a separate list of colors that describe
those fruits. They are in order, such that colors{1} describes the color of fruits{1}.
– You want to describe the name and color of each fruit, but in random order
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Permutation
■ PTB function Shuffle() will take a vector or matrix, and return to you the items in random order
■ If the input has multiple rows, each column will be shuffled, but numbers will stay in their columns. Note this multi-column shuffle does not work with cell matrices.
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>> fruits = {'apple','banana','cucumber'};>> fruits = Shuffle(fruits)
fruits =
'apple' 'cucumber' 'banana'
>> fruits = {'apple','banana','cucumber'; 'red','yellow','green'}
fruits =
'apple' 'banana' 'cucumber' 'red' 'yellow' 'green'>> fruits = Shuffle(fruits)
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Other randomization functions
■ RandSample()■ ChooseKFromN()■ RandSel()■ URandSel()■ CoinFlip()
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Priority
■ Modern computers have multiple software processes constantly competing for access to resources.
■ How these resources are allocated moment to moment can affect the execution of your script
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Priority
■ Recommendation: When you are testing with PTB, close applications other than Matlab
■ Use PTB's Priority function to assign a priority to the execution of your process
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Priority
■ Use Priority() to set the priority level■ The higher the priority level, the less chance there is of other
processes interfering with your script■ Available levels and their functions differ depending on your OS
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Priority: OSX
■ OSX: Priority levels range from 0-9 and relate to the percentage of CPU time guaranteed to the PTB thread
– However, if you use too much CPU, the OS may kick you back down to level 0
– If you frequently call WaitSecs or Flip, you are unlikely to be demoted
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Priority: Windows
■ On Windows there are 3 levels available: – 0 : normal priority level– 1: high priority level– 2: real time priority level■ Using level 2 may cause problems (for example, it may disable
keyboard input). Probably only want to use this when absolutely necessary, for example when running an intense animation where timing really matters.
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Priority
■ MaxPriority(windowOrScreenNum) will tell you the maximum priority allowed on your system
■ Not recommended to use greater than 1 on windows
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PrioritywhichScreen = max(Screen('Screens'));maxPriorityLevel = MaxPriority(whichScreen);Priority(maxPriorityLevel);
These lines would go at the beginning of your script to set priority level for that script
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Testing for OS>> IsOSX
ans =
1>> IsWindows
ans =
0
if IsOSX%OSX specific code here
elseif IsWindows%Windows specific code here
end
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Code organization
■ Functions and subfunctions■ In your script all of the following functions are available to you:– Built in Matlab functions– Any functions whose name is a filename in your current directory– Any functions whose name is a filename in another folder when that
folder is in your Path
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Functions and subfunctions
■ Outsource repeated and often-used code to its own function■ Remember variable scope! Variables that exist in one function will not
be available to another, unless you pass them as parameters
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function addEmUP(x,y)
addedUp = x + y;printItOut();
end
function printItOut
fprintf('The output is: %d\n',addedUp);
end
function addEmUP(x,y)
addedUp = x + y;printItOut(addedUp);
end
function printItOut(numToPrint)
fprintf('The output is: %d\n',numToPrint);
end
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function welcomeUser
[wPtr,rect] = Screen('OpenWindow',1);
myText = 'Welcome to my script';drawAtCenter(myText);KbWait();
myText = 'So, here we are.';drawAtCenter(myText);KbWait();
end
function drawAtCenter(theText)
DrawFormattedText(wPtr,theText,'center','center');
end
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function welcomeUser
[wPtr,rect] = Screen('OpenWindow',1);
myText = 'Welcome to my script';drawAtCenter(myText);KbWait();
myText = 'So, here we are.';drawAtCenter(wPtr,myText);KbWait();
end
function drawAtCenter(wPtr,theText)
DrawFormattedText(wPtr,theText,'center','center');
end
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Acccessing the web
■ web(url) to open url in matlab web browser■ web(url,'-browser') to open in system browser
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Invoking programs outside Matlab■ system()
>> system('open –a Textedit.app')
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Other PTB toolboxes
■ PsychGLImageProcessing■ PsychVideoCapture■ PsychColorimetric■ PsychKinect
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Final Exam■ Full Experiment. Must:– Write the entire thing from scratch yourself– Take subject code and any relevant conditions as inputs– Present repetitive trials that involve at least 2 different
conditions– Must present either visual or auditory stimuli (or both)– Must collect some kind of behavioral response where timing is
recorded– Must write responses out to a log file
Please run your experiment plan by me as soon as possible. If you don't have something you are working on now, I will make something up for you.
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